A negative electrode material, a preparation method thereof, and an electrochemical device

Abstract

The application provides a negative electrode material, a preparation method thereof, and an electrochemical device using the negative electrode material. The negative electrode material comprises: a core, wherein the core comprises silicon-based particles; a first layer comprising carbon, wherein the first layer is present outside the core; a second layer comprising a first conductive material and a metal oxide, wherein the second layer is present outside the first layer; and a third layer comprising a second conductive material and a polymer, wherein the third layer is present outside the second layer. The negative electrode material provided by the application can reduce the volume expansion of the electrochemical device after cycling and improve the cycling performance of the electrochemical device.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of electrochemical energy storage, and in particular to a negative electrode material, a preparation method thereof, and an electrochemical device using the negative electrode material. BACKGROUND

[0002] Silicon is widely used in negative electrode materials due to its high specific capacity. In addition, silicon negative electrodes have high energy density and suitable working voltage, and have broad application prospects. However, silicon expands by up to 400% after intercalating lithium, and the repeated expansion and contraction of silicon-based negative electrode materials during the cycle process can cause the destruction and growth of the solid electrolyte interface film (SEI film) and the fragmentation of silicon-based particles, resulting in huge electrode expansion and rapid capacity decay, which affects the thickness and cycle performance of the electrochemical device and restricts the large-scale application of silicon negative electrode materials in lithium ion batteries. SUMMARY

[0003] The present application aims to provide a negative electrode material, a preparation method thereof, and an electrochemical device using the negative electrode material, so as to improve the cycle performance of the electrochemical device. The specific technical solutions are as follows:

[0004] The first aspect of the present application provides a negative electrode material, which comprises: a core, the core comprising silicon-based particles; a first layer, the first layer being present outside the core; a second layer, the second layer being present outside the first layer; and a third layer, the third layer being present outside the second layer; wherein the first layer comprises carbon; the second layer comprises a first conductive material and a metal oxide; and the third layer comprises a second conductive material and a polymer. The introduction of the first layer comprising carbon can improve the problem of gas production caused by the direct contact of the silicon-based particles with water during the stirring process of preparing the slurry; the introduction of the second layer can reduce the side reaction of the negative electrode material with the electrolyte and improve the cycle performance of the lithium ion battery; the introduction of the third layer can reduce the thickness expansion rate of the lithium ion battery and reduce the specific surface area of the silicon-based particles to improve the initial efficiency of the lithium ion battery. The introduction of the first conductive material and the second conductive material can make the negative electrode material have good electrical conductivity; the synergistic effect of the three layers reduces the expansion rate of the lithium ion battery and improves the cycle performance of the lithium ion battery.

[0005] In an embodiment of the present application, the silicon-based particles comprise at least one of silicon-carbon particles or silicon-oxygen particles.

[0006] In an embodiment of the present application, the metal oxide comprises at least one of aluminum oxide or titanium oxide.

[0007] In an embodiment of the present application, the polymer comprises polyurethane.

[0008] In an embodiment of the present application, the first conductive material and the second conductive material are each independently selected from at least one of single-walled carbon nanotubes, multi-walled carbon nanotubes, and conductive carbon black.

[0009] The silicon-based particles select the material in the above range, which can make the negative electrode have a higher capacity, so that the negative electrode is applied to a lithium ion battery, which can make the lithium ion battery have a higher energy density and good cycle performance; the metal oxide selects the material in the above range, which can reduce the corrosion of the electrolyte decomposition product to the negative electrode and improve the cycle performance of the lithium ion battery; the polymer selects polyurethane, which can reduce the volume expansion of the negative electrode, reduce the thickness expansion rate of the lithium ion battery, and at the same time, the specific surface area of the negative electrode material is also reduced, thereby improving the first charge-discharge efficiency of the negative electrode material; the first conductive material and the second conductive material select the material in the above range, which can improve the problem of reduced electrical conductivity of the negative electrode material caused by the coating of the metal oxide and the polymer.

[0010] In an embodiment of the present application, the mass percentage of silicon element is 40% to 50% based on the mass of the negative electrode material. When the mass percentage of silicon element is in the above range, the lithium ion battery using the negative electrode material of the present application has a higher reversible capacity and also has good cycle performance, thereby being beneficial to improving the energy density and cycle performance of the lithium ion battery.

[0011] In an embodiment of the present application, the negative electrode material satisfies at least one of the following: (1) the Dv50 of the negative electrode material is 6 μm to 10 μm; (2) the Dv90 of the negative electrode material is less than or equal to 30 μm; (3) the mass percentage of carbon in the first layer is 1% to 5% based on the mass of the negative electrode material; (4) the mass percentage of the metal oxide is 0.2% to 1% based on the mass of the negative electrode material; (5) the mass percentage of the polymer is 0.9% to 9% based on the mass of the negative electrode material; (6) the mass percentage of the first conductive material is 0.1% to 0.4% based on the mass of the negative electrode material; and (7) the mass percentage of the second conductive material is 0.1% to 1% based on the mass of the negative electrode material. When the negative electrode material satisfies at least one of the above characteristics, the first charge-discharge efficiency of the negative electrode material is improved, and the cycle performance of the lithium ion battery is improved and the thickness expansion rate of the lithium ion battery is reduced.

[0012] In an embodiment of the present application, the mass ratio of the polymer to the second conductive material is 9:1 to 9:2. When the mass ratio of the polymer to the second conductive material is in the above range, the negative electrode material has good performance and also has good conductivity efficiency.

[0013] The second aspect of the present application provides a preparation method of the negative electrode material provided by the first aspect of the present application, which comprises: providing silicon-based particles; performing carbon coating on the silicon-based particles to obtain a first intermediate; dispersing the first intermediate, a metal alkoxide, polyvinylpyrrolidone and a first conductive material in ethanol to obtain a first dispersion, fully dispersing and stirring the first dispersion, and obtaining a second intermediate through spray drying and heat treatment at 500-600 DEG C, wherein the metal alkoxide comprises at least one of aluminum isopropoxide or titanium isopropoxide; dispersing the second intermediate in water to obtain a second dispersion, dispersing a polymer and a second conductive material in water to obtain a third dispersion, mixing and uniformly stirring the second dispersion and the third dispersion, and obtaining the negative electrode material through spray drying. The preparation method has simple steps and is easy to operate, and is suitable for industrial production. The coating can be partial coating or full coating.

[0014] In an embodiment of the present application, the carbon coating is performed by placing the silicon-based particles in a fluidized bed, introducing a carbon source gas at a temperature of 500-600 DEG C, and reacting for 2-3 h to obtain the first intermediate, wherein the carbon source gas comprises at least one of acetylene, methane or propylene. When the reaction temperature and the reaction time are in the above range, the carbon source gas can be cracked at a faster rate and deposited on the outside of the silicon-based particles at a higher utilization rate.

[0015] The third aspect of the present application provides an electrochemical device, which comprises a positive electrode, a separator, an electrolyte and a negative electrode, wherein the negative electrode comprises a negative electrode active material layer, and the negative electrode active material layer comprises the negative electrode material provided by the first aspect of the present application.

[0016] In an embodiment of the present application, the electrolyte comprises an additive, and the additive comprises at least one of 1,3,6-hexanetricarbonitrile, 1,2,3-propanetricarbonitrile or 1,2,3-tris(2-cyanato)propane, wherein the mass percentage of the additive is 0.1-5% based on the total mass of the electrolyte. When the mass percentage of the additive is in the above range, the corrosion of the electrolyte decomposition product to the negative electrode active material can be improved, and the high-temperature storage performance of the lithium ion battery can be improved.

[0017] The fourth aspect of the present application provides a power utilization device, which comprises the electrochemical device provided by the third aspect of the present application.

[0018] The beneficial effects of the present application are as follows:

[0019] The negative electrode material provided by the application comprises a first layer of carbon, which can improve the problem of gas production caused by direct contact of the silicon-based particles with water during contact with an aqueous solvent. The second layer can reduce direct contact of the electrolyte with the silicon-based particles, reduce side reactions between the negative electrode material and the electrolyte, and thus improve the cycle performance of the lithium ion battery. Moreover, the second layer can improve the composition of the SEI film, thereby improving the cycle performance of the lithium ion battery. The third layer can form a stable coating layer through its good adhesion, and cooperates with the first layer and the second layer to form the negative electrode material, reduce the volume expansion of the negative electrode, reduce the thickness expansion rate of the lithium ion battery, and can reduce the specific surface area of the silicon-based particles, and improve the first charge-discharge efficiency of the negative electrode material. In addition, the introduction of the first conductive material and the second conductive material can make the negative electrode material have good conductivity. Therefore, the negative electrode material provided by the application reduces the expansion rate of the lithium ion battery and improves the cycle performance of the lithium ion battery through the synergistic effect of the three coating layers. BRIEF DESCRIPTION OF DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the application, and other embodiments can also be obtained by those skilled in the art based on these drawings.

[0021] Figure 1 Structure schematic diagram of the negative electrode material prepared for the embodiment 1 of the application;

[0022] Figure 2 Cycle performance comparison diagram of the lithium ion batteries assembled by the negative electrode materials in the embodiment 1-1 and the comparative examples 1 to 3 at 25℃;

[0023] Figure 3 Cycle performance comparison diagram of the lithium ion batteries assembled by the negative electrode materials in the embodiment 1-1 and the comparative examples 1 to 3 at 45℃;

[0024] Figure 4 Expansion rate comparison diagram of the lithium ion batteries assembled by the negative electrode materials in the embodiment 1-1 and the comparative examples 1 to 3 at 25℃;

[0025] Figure 5 Expansion rate comparison diagram of the lithium ion batteries assembled by the negative electrode materials in the embodiment 1-1 and the comparative examples 1 to 3 at 45℃. DETAILED DESCRIPTION

[0026] The technical solutions in the embodiments of the present application will be clearly and completely described below. Obviously, the described embodiments are only some of the embodiments of the present application, but not all of the embodiments. All other embodiments obtained by those skilled in the art based on the present application shall fall within the scope of the present application.

[0027] It should be noted that in the specific embodiments of the present application, the present application is explained by taking lithium ion batteries as examples of electrochemical devices, but the electrochemical devices of the present application are not limited to lithium ion batteries.

[0028] The first aspect of the present application provides a negative electrode material, comprising: a core, the core comprising silicon-based particles; a first layer, the first layer existing outside the core; a second layer, the second layer existing outside the first layer; a third layer, the third layer existing outside the second layer; wherein the first layer comprises carbon; the second layer comprises a first conductive material and a metal oxide; and the third layer comprises a second conductive material and a polymer. In the present application, the first layer exists outside the entire core or part of the core, the second layer exists outside the entire first layer or part of the first layer, and the third layer exists outside the entire second layer or part of the second layer. Specifically, the structural schematic diagram of the negative electrode material is as shown in Figure 1 The mutual solubility layer is not the first layer, the second layer or the third layer described in the present application.

[0029] Without being limited to any theory, the inventors of the present application found that the introduction of the carbon-containing first layer can improve the gas production problem caused by the direct contact of the silicon-based particles with water during the contact with the aqueous solvent. The introduction of the second layer can reduce the direct contact of the electrolyte with the silicon-based particles, reduce the side reaction of the negative electrode material with the electrolyte, thereby improving the cycle performance of the lithium ion battery; and the introduction of the second layer can improve the composition of the SEI film, thereby improving the cycle performance of the lithium ion battery. The introduction of the third layer can form a stable coating layer through its good adhesion, and the first layer and the second layer together form a negative electrode material, reduce the volume expansion of the negative electrode, reduce the thickness expansion rate of the lithium ion battery, and can reduce the specific surface area of the silicon-based particles, improve the first charge-discharge efficiency of the negative electrode material. In addition, the introduction of the first conductive material and the second conductive material can make the negative electrode material have good conductivity. Therefore, the negative electrode material provided by the present application reduces the expansion rate of the lithium ion battery through the synergistic effect of the three coating layers, and improves the cycle performance of the lithium ion battery.

[0030] In an embodiment of the present application, the silicon-based particles comprise at least one of silicon-carbon particles or silicon-oxygen particles.

[0031] In an embodiment of the present application, the metal oxide comprises at least one of aluminum oxide or titanium oxide.

[0032] In an embodiment of the present application, the polymer comprises polyurethane.

[0033] In an embodiment of the present application, the first conductive material and the second conductive material are each independently selected from at least one of single-walled carbon nanotubes, multi-walled carbon nanotubes, or conductive carbon black.

[0034] Without being limited to any theory, the inventors of the present application found that, by selecting the silicon-based particles to be materials within the above-mentioned range, the negative electrode can have a higher capacity, and thus, when the negative electrode is applied to a lithium ion battery, the lithium ion battery can have a higher energy density; by selecting the metal oxide to be a material within the above-mentioned range, the corrosion of the negative electrode by electrolyte decomposition products can be reduced, and the cycle performance of the lithium ion battery can be improved; by selecting the polymer to be polyurethane, the polymer has good adhesion, can form a stable coating layer, and can bond the second intermediate together to form the negative electrode material, which can reduce the volume expansion of the negative electrode, thereby reducing the thickness expansion rate of the lithium ion battery, and at the same time, the specific surface area of the negative electrode material is also reduced, which improves the first charge-discharge efficiency of the negative electrode material; by selecting the first conductive material and the second conductive material to be materials within the above-mentioned range, the negative electrode material can have good electrical conductivity.

[0035] In an embodiment of the present application, the silicon-based particles satisfy at least one of the following: (1) the specific surface area of the silicon-based particles is 0.5 m 2 / g to 10 m 2 / g; (2) the particle size Dv50 of the silicon-based particles is 1.5 μm to 2.5 μm; (3) the particle size Dv90 of the silicon-based particles is less than or equal to 10 μm. The particle classification technology is not particularly limited in the present application, as long as the purpose of the present application can be achieved, and the particle classification technology can be any known classification means in the art, such as fluidized classification and cyclone classification. In the present application, Dv50 refers to the particle size at which 50% of the volume of the material is accumulated, measured from small particle size; and Dv90 refers to the particle size at which 90% of the volume of the material is accumulated, measured from small particle size.

[0036] In an embodiment of the present application, the specific surface area of the silicon-based particles can be 0.5 m 2 / g, 1 m 2 / g, 2 m 2 / g, 3 m 2 / g, 4 m 2 / g, 5 m 2 / g, 6m 2 / g, 7m 2 / g, 8m 2 / g, 9m 2 / g, 10m 2 / g, or a range formed by any two of the numerical values; the shape of the silicon-based particles can be at least one of spherical, spheroidal, flaky, or massive; without being limited by any theory, the inventors of the present application have found that when the specific surface area of the silicon-based particles is 0.5m 2 / g to 10m 2 / g, the problem of gas generation caused by direct contact of the silicon-based particles with water during stirring with an aqueous solvent can be improved, and at the same time, a higher coating degree of the subsequent coating layer can be achieved.

[0037] In an embodiment of the present application, the particle size Dv50 of the silicon-based particles can be 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, 2 μm, 2.1 μm, 2.2 μm, 2.3 μm, 2.4 μm, 2.5 μm, or a range formed by any two of the numerical values; without being limited by any theory, the inventors of the present application have found that when the particle size Dv50 of the silicon-based particles is 1.5 μm to 2.5 μm, the diffusion path of Li + is shorter, which can improve the ionic conductivity of the negative electrode material and reduce the volume expansion of the silicon-based particles.

[0038] In an embodiment of the present application, the particle size Dv90 of the silicon-based particles can be 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, or a range formed by any two of the numerical values; without being limited by any theory, the inventors of the present application have found that when the particle size Dv90 of the silicon-based particles is less than or equal to 10 μm, the silicon-based particles are uniformly dispersed during the coating process, thereby controlling the particle size of the negative electrode material, so that when the negative electrode material is used in the negative electrode, the transmission of Li + is improved, thereby improving the cycle performance and expansion performance of the lithium ion battery.

[0039] In an embodiment of the present application, the mass percentage content of silicon element based on the mass of the negative electrode material is 40% to 50%. For example, the mass percentage content of silicon element can be 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, or a range formed by any two of the numerical values. Without being limited by any theory, the inventors of the present application have found that when the mass percentage content of silicon element is 40% to 50%, the negative electrode material has a higher reversible capacity and first charge-discharge efficiency, and is beneficial to improving the energy density and cycle performance of the lithium ion battery.

[0040] In an embodiment of the present application, the particle size Dv50 of the negative electrode material is 6-10 μm. For example, the particle size Dv50 of the negative electrode material can be 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm, 10 μm, or a range defined by any two of the above values. Without being limited to any theory, the inventors of the present application have found that by controlling the particle size Dv50 of the negative electrode material to be 6-10 μm, the diffusion path of Li + is shorter, thereby improving the ionic conductivity of Li + , which can improve the initial charge-discharge efficiency of the negative electrode material; at the same time, it can also reduce the consumption of electrolyte, increase the compaction density of the material, and make the negative electrode material have higher ionic conductivity and higher rate capability, thereby improving the energy density and cycle performance of the lithium ion battery.

[0041] In an embodiment of the present application, the particle size Dv90 of the negative electrode material is less than or equal to 30 μm. For example, the particle size Dv90 of the negative electrode material can be 12 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, 21 μm, 22 μm, 23 μm, 24 μm, 25 μm, 26 μm, 27 μm, 28 μm, 29 μm, 30 μm, or a range defined by any two of the above values. Without being limited to any theory, the inventors of the present application have found that by controlling the particle size Dv90 of the negative electrode material to be less than or equal to 30 μm, the dispersion uniformity of the negative electrode material in the preparation of the negative electrode slurry can be improved, the consistency of the negative electrode sheet coating weight and thickness can be improved, the expansion and contraction of each layer of the negative electrode sheet during the charge-discharge cycle process can be more consistent, at the same time, the stress distribution caused by the expansion and contraction can be more consistent, the possibility of stress concentration leading to the peeling of the negative electrode material layer from the current collector can be reduced, thereby improving the cycle performance and expansion performance of the lithium ion battery.

[0042] In an embodiment of the present application, the mass percentage of carbon in the first layer is 1-5% based on the mass of the negative electrode material. For example, the mass percentage of carbon in the first layer can be 1%, 1.5%, 2%, 2.5%, 3%, 4%, 4.5%, 5%, or a range defined by any two of the above values. When the mass percentage of carbon in the first layer is within the above range, the contact between the active silicon in the silicon-based particles and air or solution can be effectively reduced, and the active silicon can be protected, which can enable the negative electrode material to have higher specific capacity and stability, thereby improving the cycle stability and capacity of the lithium ion battery.

[0043] In an embodiment of the present application, the mass percentage of the metal element in the metal oxide is 0.2% to 1% based on the mass of the negative electrode material. For example, the mass percentage of the metal oxide can be 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, or a range between any two of the values. When the mass percentage of the metal oxide is within the above range, the composition of the SEI film can be improved, the corrosion of the electrolyte decomposition product to the negative electrode can be reduced, and the cycle performance of the lithium ion battery can be improved.

[0044] In an embodiment of the present application, the mass percentage of the polymer is 0.9% to 9% based on the mass of the negative electrode material. For example, the mass percentage of the polymer can be 0.9%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or a range between any two of the values. When the mass percentage of the polymer is within the above range, a stable coating layer can be formed by its good adhesion, and the second intermediate body can be bonded together to form the negative electrode material, the volume expansion of the negative electrode can be reduced, the thickness expansion rate of the lithium ion battery can be reduced, and the specific surface area of the negative electrode material can also be reduced.

[0045] In an embodiment of the present application, the mass percentage of the first conductive material is 0.1% to 0.4% based on the mass of the negative electrode material. For example, the mass percentage of the first conductive material can be 0.1%, 0.2%, 0.3%, 0.4%, or a range between any two of the values. When the mass percentage of the first conductive material is within the above range, the negative electrode material can have good conductivity while introducing the second layer of the metal oxide.

[0046] In an embodiment of the present application, the mass percentage of the second conductive material is 0.1% to 1% based on the mass of the negative electrode material. For example, the mass percentage of the second conductive material can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, or a range between any two of the values. When the mass percentage of the second conductive material is within the above range, the negative electrode material can have good conductivity while introducing the third layer containing the polymer.

[0047] In an embodiment of the present application, the mass ratio of the polymer to the second conductive material is 9:1 to 9:2. For example, the mass ratio of the second conductive material to the polymer can be 9:1, 9:1.1, 9:1.2, 9:1.3, 9:1.4, 9:1.5, 9:1.6, 9:1.7, 9:1.8, 9:1.9, 9:2, or a range defined by any two of the above values. When the mass ratio of the polymer to the second conductive material is within the above range, the polymer is better adhered to the second intermediate body through its better adhesion, a stable coating layer is formed, and the second intermediate body is adhered together to form the negative electrode material, which reduces the volume expansion of the negative electrode while the negative electrode material has good conductivity, thereby reducing the thickness expansion rate of the lithium ion battery.

[0048] The second aspect of the present application provides a preparation method of the negative electrode material provided by the first aspect of the present application, which comprises: providing silicon-based particles; carbon-coating the silicon-based particles to obtain a first intermediate body; dispersing the first intermediate body, an organic metal salt, polyvinylpyrrolidone, and a first conductive material in ethanol to obtain a first dispersion, fully dispersing and stirring the first dispersion, and obtaining a second intermediate body by spray drying and heat treatment at 500-600°C, wherein the organic metal salt comprises at least one of aluminum isopropoxide or titanium isopropoxide; dispersing the second intermediate body in water to obtain a second dispersion, dispersing a polymer and a second conductive material in water to obtain a third dispersion, mixing and uniformly stirring the second dispersion and the third dispersion, and obtaining the negative electrode material by spray drying. The above preparation method is simple in steps, easy to operate, and suitable for industrial production.

[0049] In an embodiment of the present application, the carbon coating is performed by placing the silicon-based particles in a fluidized bed, passing a carbon source gas at a temperature of 500-650°C, and reacting for 2-3h to obtain the first intermediate body, wherein the carbon source gas comprises at least one of acetylene, methane, and propylene. For example, the coating temperature can be 500°C, 510°C, 520°C, 530°C, 540°C, 650°C, 560°C, 570°C, 580°C, 590°C, 600°C, 610°C, 620°C, 630°C, 640°C, 650°C, or a range defined by any two of the above values; the coating time can be 2h, 2.2h, 2.4h, 2.6h, 2.8h, 3h, or a range defined by any two of the above values. Without being limited to any theory, the present inventors have found that the carbon source gas is deposited on the outside of the target particles after cracking at high temperature, and within a suitable temperature range, the higher the deposition temperature, the faster the cracking rate and the higher the utilization rate of the carbon source gas, and the faster the growth rate of the coating layer; at the same deposition temperature, the length of the deposition time determines the thickness and integrity of the coating layer. By controlling the time and temperature of the carbon coating, the content of the carbon material in the carbon coating process can be controlled.

[0050] In an embodiment of the present application, the carbon source gas and the inert gas are mixed and then introduced into the fluidized bed, the inert gas comprising at least one of nitrogen or argon; the volume percentage of the carbon source gas in the mixed gas is 10% to 50% based on the volume of the mixed gas. For example, the volume percentage of the carbon source gas can be 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, or a range defined by any two of the above values. Without being limited to any theory, the inventors of the present application have found that the provision of the inert gas is conducive to improving the uniformity of the distribution of carbon elements in the shell.

[0051] In an embodiment of the present application, the Dv50 of the first intermediate is 1.5 μm to 2.5 μm. For example, the particle size Dv50 can be 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, 2 μm, 2.1 μm, 2.2 μm, 2.3 μm, 2.4 μm, 2.5 μm, or a range defined by any two of the above values.

[0052] In an embodiment of the present application, the mass ratio of the first intermediate, the organic metal salt, the polyvinylpyrrolidone, and the first conductive material is 100:(0.4 to 4):(0.4 to 4):(0.11 to 0.44). Without being limited to any theory, the inventors of the present application have found that when the mass ratio of the first intermediate, the organic metal salt, the polyvinylpyrrolidone, and the first conductive material is within the above range, the organic metal salt and the first conductive material can be better coated outside the first intermediate under the binding action of the polyvinylpyrrolidone.

[0053] In an embodiment of the present application, the solid content of the first dispersion is 18% to 22%. For example, the solid content of the first dispersion can be 18%, 19%, 20%, 21%, 22%, or a range defined by any two of the above values.

[0054] In an embodiment of the present application, the ratio of the mass of the first intermediate to the sum of the mass of the mixture of the metal oxide and the first conductive material is 100:1 to 100:4. For example, the ratio of the mass of the first intermediate to the sum of the mass of the mixture of the metal oxide and the first conductive material can be 100:1, 100:1.5, 100:2, 100:2.5, 100:3, 100:3.5, 100:4, or a range defined by any two of the above values. Without being limited to any theory, the inventors of the present application have found that when the ratio of the mass of the first intermediate to the sum of the mass of the mixture of the metal oxide and the first conductive material is 100:1 to 100:4, the corrosion of the electrolyte decomposition product to the negative electrode material can be reduced, the cycle performance of the lithium ion battery can be improved, and at the same time, the silicon content of the negative electrode material can be within the range of the present application, so that the negative electrode material has a higher reversible capacity.

[0055] In an embodiment of the present application, the inlet air temperature of the spray drying of the second intermediate is 170-190°C, and the outlet air temperature is 90-100°C. Without being limited by any theory, the present inventors have found that when the parameters of the spray drying are within the above ranges, the particle size distribution of the second intermediate after spray drying can be controlled while taking into account the drying capacity of the equipment and the production capacity, and meanwhile, the increase in particle size caused by the agglomeration of particles can be reduced.

[0056] In an embodiment of the present application, the heat treatment of the second intermediate at 500-600°C is performed by placing the dried first intermediate coated with aluminum isopropoxide and polyvinylpyrrolidone into a graphite crucible, placing the crucible in a box furnace, passing nitrogen at a flow rate of 1.5-2.5 L / min for 20-40 min after closing the door of the furnace, then turning on the heating, heating at a rate of 5-10°C / min to 500-600°C, and then holding for 0.5-3 h, turning off the heating and continuing to pass nitrogen to cool to room temperature, and then taking out the crucible to obtain the second intermediate.

[0057] In an embodiment of the present application, the Dv50 of the second intermediate is 1.6-2.7 μm. For example, the particle size Dv50 can be 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, 2 μm, 2.1 μm, 2.2 μm, 2.3 μm, 2.4 μm, 2.5 μm, 2.6 μm, 2.7 μm, or a range defined by any two of the above values.

[0058] In an embodiment of the present application, the solid content of the second dispersion is 20-35%. For example, the solid content of the second dispersion can be 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, or a range defined by any two of the above values.

[0059] In an embodiment of the present application, the mass ratio of the polymer and the second conductive material is 9:1-9:2. For example, the mass ratio of the polymer and the second conductive material can be 9:1, 9:1.1, 9:1.2, 9:1.3, 9:1.4, 9:1.5, 9:1.6, 9:1.7, 9:1.8, 9:1.9, 9:2, or a range defined by any two of the above values. Without being limited by any theory, the present inventors have found that the introduction of the conductive material can alleviate the problem of reduced electrical conductivity of the negative electrode material caused by the polymer coating.

[0060] In an embodiment of the present application, the solid content of the third dispersion is 18-22%. For example, the solid content of the third dispersion can be 18%, 18.5%, 19%, 19.5%, 20%, 20.5%, 21%, 21.5%, 22%, or a range defined by any two of them.

[0061] In an embodiment of the present application, the ratio of the mass of the second intermediate to the mass of the mixture of the binder and the second conductive material is 100:1-100:10. For example, the ratio of the mass of the second intermediate to the mass of the mixture of the binder and the second conductive material can be 100:1, 100:2, 100:3, 100:4, 100:5, 100:6, 100:7, 100:8, 100:9, 100:10, or a range defined by any two of them; without being limited by any theory, the present inventors have found that when the ratio of the mass of the second intermediate to the mass of the mixture of the polymer and the second conductive material is 100:1-100:10, the volume expansion of the negative electrode material is reduced due to the better adhesion of the polymer, the thickness expansion rate of the lithium ion battery is reduced, the specific surface area of the negative electrode material is reduced, the first charge-discharge efficiency is improved, and the addition of the conductive material can alleviate the problem of reduced electrical conductivity of the negative electrode material caused by the polyurethane coating.

[0062] In an embodiment of the present application, the solid content of the mixed slurry after mixing the second dispersion and the third dispersion is 20%-25%. For example, the solid content of the mixed slurry after mixing the second dispersion and the third dispersion can be 20%, 21%, 22%, 23%, 24%, 25%, or a range defined by any two of them.

[0063] In an embodiment of the present application, the inlet air temperature of the spray drying of the negative electrode material is 200-230°C, and the outlet air temperature is 100-110°C. Without being limited by any theory, the present inventors have found that when the parameters of the spray drying are within the above ranges, the particle size distribution of the negative electrode material after spray drying can be controlled while taking into account the drying capacity of the machine and the production capacity.

[0064] In an embodiment of the present application, the coating referred to in the present application can be partial coating or complete coating.

[0065] The third aspect of the present application provides an electrochemical device comprising a positive electrode, a separator, an electrolyte, and a negative electrode, wherein the negative electrode comprises a negative electrode active material layer, and the negative electrode active material layer comprises the negative electrode material of the first aspect of the present application.

[0066] In one embodiment of the present application, the electrolyte comprises an additive, the additive comprises at least one of 1,3,6-hexanetricarbonitrile, 1,2,3-propanetricarbonitrile or 1,2,3-tris(2-cyanato)propane, and the mass percentage of the additive is 0.1% to 5% based on the total mass of the electrolyte. For example, the mass percentage of the additive can be 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4.5%, 5% or a range between any two of them. Without being limited to any theory, the inventors of the present application have found that the above-mentioned additive can reduce the reactivity of the positive electrode transition metal, thereby reducing the degradation of the electrolyte during the cycle process, greatly improving the corrosion of the electrolyte decomposition products to the negative active material, and achieving the effect of improving the high-temperature storage performance of the lithium ion battery.

[0067] In the present application, the electrolyte further comprises a lithium salt, which is not particularly limited in the present application, and any lithium salt known in the art can be used as long as the purpose of the present application can be achieved. For example, the lithium salt can be selected from at least one of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3and LiPO2F2. The mass percentage of the lithium salt can be 8% to 15% based on the mass of the electrolyte, for example, the mass percentage of the lithium salt can be 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15% or a range between any two of them.

[0068] In the present application, the electrolyte further comprises a base solvent, which is not particularly limited in the present application, and any base solvent known in the art can be used as long as the purpose of the present application can be achieved, for example, the base solvent can include but is not limited to at least one of carbonate compounds, carboxylate compounds, ether compounds or other organic solvents.

[0069] The carbonate compound can include, but is not limited to, at least one of a chain carbonate compound, a cyclic carbonate compound, or a fluoro-carbonate compound. The chain carbonate compound can include, but is not limited to, at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), or methyl ethyl carbonate (MEC). The cyclic carbonate compound can include, but is not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), or vinyl ethylene carbonate (VEC). The fluoro-carbonate compound can include, but is not limited to, at least one of 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methyl ethylene carbonate, 1-fluoro-1-methyl ethylene carbonate, 1,2-difluoro-1-methyl ethylene carbonate, 1,1,2-trifluoro-2-methyl ethylene carbonate, or trifluoromethyl ethylene carbonate. The carboxylic acid ester compound can include, but is not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, t-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolactone, valerolactone, or caprolactone. The ether compound can include, but is not limited to, at least one of dibutyl ether, tetraglyme, diglyme, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran, or tetrahydrofuran. The other organic solvent can include, but is not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate. The content of the base solvent in the electrolyte is not particularly limited in the present application, as long as the object of the present application is achieved.

[0070] In the present application, the electrochemical device further includes a cathode including a cathode current collector and a cathode active material layer disposed on at least one surface of the cathode current collector. The "cathode active material layer disposed on at least one surface of the cathode current collector" means that the cathode active material layer can be disposed on one surface of the cathode current collector in the thickness direction thereof, or can be disposed on both surfaces of the cathode current collector in the thickness direction thereof. It is noted that the "surface" herein can be the entire area of the surface of the cathode current collector, or can be a partial area of the surface of the cathode current collector, and the present application is not particularly limited, as long as the object of the present application is achieved.

[0071] The cathode current collector is not particularly limited in the present application, as long as the object of the present application is achieved, and for example, can include an aluminum foil, an aluminum alloy foil, or a composite current collector (e.g., an aluminum-carbon composite current collector), etc.

[0072] The positive electrode active material is not particularly limited as long as the object of the present application can be achieved, for example, the positive electrode active material can include, but is not limited to, at least one of lithium cobaltate, lithium nickel-manganese-cobaltate, lithium nickel-manganese-aluminate, lithium iron phosphate, lithium vanadium phosphate, lithium cobalt phosphate, lithium manganese phosphate, lithium manganese iron phosphate, lithium iron silicate, lithium vanadium silicate, lithium cobalt silicate, lithium manganese silicate, spinel lithium manganate, spinel lithium nickel-manganese phosphate, and lithium titanate.

[0073] The positive electrode material layer can further include a conductive agent and a binder, and the kind of the conductive agent and the binder is not particularly limited as long as the object of the present application can be achieved. The mass ratio of the positive electrode active material, the conductive agent, and the binder in the positive electrode material layer is not particularly limited, and can be selected by those skilled in the art according to actual needs as long as the object of the present application can be achieved.

[0074] The binder is not particularly limited as long as the object of the present application can be achieved, for example, the binder can include, but is not limited to, at least one of an adhesive polymer such as polyvinylidene fluoride, polytetrafluoroethylene, polyolefin, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, modified polyvinylidene fluoride, modified SBR rubber, or polyurethane, wherein the polyolefin binder includes at least one of polyethylene, polypropylene, polyolefin ester, polyolefin alcohol, or polyacrylic acid.

[0075] The conductive agent is not particularly limited as long as the object of the present application can be achieved, for example, the conductive agent can include, but is not limited to, a carbon-based material, a metal-based material, a conductive polymer, or a mixture thereof; wherein the carbon-based material includes natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, or carbon fiber; the metal-based material includes metal powder or metal fiber of copper, nickel, aluminum, silver, etc.; and the conductive polymer includes polyphenylene derivative.

[0076] The thickness of the positive electrode current collector and the positive electrode material layer is not particularly limited as long as the object of the present application can be achieved. For example, the thickness of the positive electrode current collector is 5 μm to 20 μm, and the thickness of the single-sided positive electrode material layer is 30 μm to 120 μm.

[0077] Optionally, the positive electrode can further include a conductive layer, and the conductive layer is located between the positive electrode current collector and the positive electrode material layer. The composition of the conductive layer is not particularly limited, and can be a commonly used conductive layer in the art. The conductive layer includes a conductive agent and a binder. The conductive agent and the binder in the conductive layer are not particularly limited, for example, can be at least one of the above-mentioned conductive agent and the above-mentioned binder.

[0078] In the present application, the electrochemical device further includes a separator film. The present application does not particularly limit the separator film as long as the purpose of the present application can be achieved. For example, the material of the separator film can include, but is not limited to, at least one of polyethylene (PE), polyolefin (PO) based on polypropylene (PP), polyester (for example, polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, or aramid. The type of the separator film can include at least one of a woven film, a nonwoven film, a microporous film, a composite film, a calendered film, or a spunlaid film.

[0079] In some embodiments of the present application, the separator film can include a base layer and a surface treatment layer. The base layer can be a nonwoven fabric, a film, or a composite film having a porous structure, and the material of the base layer can include at least one of polyethylene, polypropylene, polyethylene terephthalate, or polyimide. Optionally, a polypropylene porous film, a polyethylene porous film, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite film can be used. Optionally, a surface treatment layer is provided on at least one surface of the base layer, and the surface treatment layer can be a polymer layer or an inorganic layer, or a layer formed by mixing a polymer and an inorganic substance.

[0080] In some embodiments of the present application, the inorganic layer includes inorganic particles and a binder. The present application does not particularly limit the inorganic particles, and for example, the inorganic particles can include at least one of alumina, silica, magnesia, titania, hafnia, tin oxide, ceria, nickel oxide, zinc oxide, calcium oxide, zirconia, yttria, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. The present application does not particularly limit the binder, and for example, the binder can be at least one of the above-described binders. In some embodiments of the present application, the polymer layer includes a polymer, and the material of the polymer includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylic acid salt, polyvinylpyrrolidone, polyvinyl ether, or polyvinylidene fluoride or poly(vinylidene fluoride-hexafluoropropylene).

[0081] In some embodiments of the present application, the inorganic layer can further include a thickening agent and a wetting agent, and the present application does not particularly limit the kind of the thickening agent and the wetting agent as long as the purpose of the present application can be achieved. For example, the thickening agent can include, but is not limited to, at least one of sodium carboxymethyl cellulose or lithium carboxymethyl cellulose; and the wetting agent can include, but is not limited to, at least one of dimethylsiloxane, sodium dodecyl sulfate, trialkyl phosphate, decanoic acid methyl ester, or dodecyl acetate.

[0082] In the present application, the thickness of the separator film is not particularly limited as long as the purpose of the present application can be achieved, and for example, the thickness of the separator film can be 4 μm to 30 μm.

[0083] In the present application, the electrochemical device further includes a negative electrode including a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector. The above-mentioned "negative electrode active material layer disposed on at least one surface of the negative electrode current collector" means that the negative electrode active material layer can be disposed on one surface of the negative electrode current collector in the thickness direction of the negative electrode current collector, or can be disposed on both surfaces of the negative electrode current collector in the thickness direction of the negative electrode current collector. It should be noted that the "surface" herein can be the entire area of the surface of the negative electrode current collector, or can be part of the area of the surface of the negative electrode current collector, and the present application does not have a particular limitation, as long as the purpose of the present application can be achieved.

[0084] The present application does not have a particular limitation on the negative electrode current collector, as long as the purpose of the present application can be achieved, for example, it can include a copper foil, a copper alloy foil, a nickel foil, a stainless steel foil, a titanium foil, a nickel foam, a copper foam, or a composite current collector, and exemplarily, the composite current collector can be a lithium-copper composite current collector, a carbon-copper composite current collector, a nickel-copper composite current collector, a titanium-copper composite current collector, etc.

[0085] In some embodiments of the present application, the negative electrode active material layer can further include a conductive agent and a binder, and the present application does not have a particular limitation on the types of the conductive agent and the binder, as long as the purpose of the present application can be achieved. For example, the binder can include, but is not limited to, at least one of polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, an ethylene oxide-containing polymer, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, butadiene-styrene rubber, acrylated butadiene-styrene rubber, acrylated butadiene-styrene rubber, epoxy resin, or nylon. The conductive agent can include, but is not limited to, a carbon-based material, a metal-based material, a conductive polymer, and a mixture thereof. Among them, the carbon-based material includes at least one of natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber; the metal-based material includes at least one of metal powder, metal fiber, copper, nickel, aluminum, or silver; and the conductive polymer includes a polyphenylene derivative. The present application does not have a particular limitation on the mass ratio of the negative electrode material, the conductive agent, and the binder in the negative electrode active material layer, and a person skilled in the art can select according to the actual needs, as long as the purpose of the present application can be achieved.

[0086] The present application does not have a particular limitation on the thickness of the negative electrode active material layer, as long as the purpose of the present application can be achieved, for example, the thickness of the single-sided negative electrode active material layer is 30 μm to 120 μm.

[0087] The present application does not have a particular limitation on the thickness of the negative electrode current collector, as long as the purpose of the present application can be achieved, for example, the thickness of the negative electrode current collector is 4 μm to 15 μm.

[0088] The electrochemical device further includes a case for accommodating the positive electrode, the separator, the negative electrode, and the electrolyte solution, and other components known in the art of electrochemical devices, and the present application does not limit the other components. The case is not particularly limited in the present application, and can be a case known in the art as long as the purpose of the present application is achieved. For example, the case can be a hard case or a flexible case. The material of the hard case can be a metal, and the kind of the metal is not limited in the present application, and a metal hard case known in the art can be used as long as the purpose of the present application is achieved. The flexible case can be a metal film such as an aluminum film, a steel film, or the like.

[0089] The preparation process of the electrochemical device of the present application is well known to those skilled in the art, and the present application is not particularly limited. For example, the preparation process of the electrochemical device can include, but is not limited to, the following steps: stacking the positive electrode, the separator, and the negative electrode in order, and performing operations such as winding, folding, or the like as needed to obtain an electrode assembly having a wound structure, placing the electrode assembly in the case, injecting the electrolyte solution into the case and sealing it to obtain the electrochemical device. Alternatively, the positive electrode, the separator, and the negative electrode are stacked in order, and then the four corners of the entire stack structure are fixed with a tape to obtain an electrode assembly having a stack structure, the electrode assembly is placed in the case, the electrolyte solution is injected into the case and sealed to obtain the electrochemical device. In addition, a current protection element, a guide plate, or the like can be placed in the case as needed to prevent the pressure inside the electrochemical device from rising and overcharging or discharging.

[0090] The fourth aspect of the present application provides a power consuming device including the electrochemical device of the third aspect of the present application.

[0091] The power consuming device of the present application is not particularly limited, and can be any power consuming device known in the art. In some embodiments, the power consuming device can include, but is not limited to, a notebook computer, a pen input computer, a mobile computer, an electronic book player, a portable telephone, a portable facsimile machine, a portable copying machine, a portable printer, a headphone, a video recorder, a liquid crystal television, a portable cleaner, a portable CD player, a mini disc, a transceiver, an electronic organizer, a calculator, a memory card, a portable audio player, a radio, a backup power supply, an electric motor, an automobile, a motorcycle, a power-assisted bicycle, a bicycle, a lighting appliance, a toy, a game machine, a timepiece, a power tool, a flashlight, a camera, a household large storage battery, and a lithium ion capacitor, or the like.

[0092] Embodiments

[0093] Hereinafter, embodiments and comparative examples are presented to more specifically describe the embodiments of the present application. Various tests and evaluations were performed according to the following methods. In addition, unless otherwise specified, "parts" and "%" are on a mass basis.

[0094] Test methods and apparatus

[0095] Si element content test

[0096] Preparation of digestion sample: take 0.1000 g of silicon-based particles or negative electrode material, put it into a nickel crucible, cover the crucible cover after adding 1.5 g of KOH, and heat the muffle furnace to 400℃. The temperature rising program is to rise from room temperature to 300℃ in 2h, and then to rise from 300℃ to 400℃ in 2h. Then start to cool down, naturally cool down to 80℃, end the digestion program, take out the crucible, cool down to room temperature, take out the digested sample and put it in a polytetrafluoroethylene beaker.

[0097] Titration of sodium hydroxide standard solution of the digested sample: add 30mL of boiling water in a polytetrafluoroethylene beaker, leach for 1h, then use tweezers to clean the crucible, control the volume to 50mL, then filter the above solution into a 400mL beaker. After filtration is completed, add 20mL of concentrated nitric acid to the beaker at one time to neutralize the solution, so that the solution is acidic. After the solution cools to room temperature, add solid KCl to saturation with constant stirring, and add 2g in excess. Then add 10mL of 200g / L potassium fluoride solution, a white precipitate appears, age for 15min, filter with medium-speed quantitative filter paper, wash the beaker and precipitate with 8mL of potassium chloride solution each time, a total of three times. Take out the filter paper and put it back into the original beaker, add 20mL of potassium chloride ethanol solution, 10 drops of phenolphthalein, then neutralize the residual acid with sodium hydroxide standard solution, stir the filter paper and the scrubbing cup wall until the solution is light red, in the process, use a glass rod to stir the paper pulp, react for 1h. Add 200mL of neutralized boiling water to the cup (boil and add 10 drops of phenolphthalein, neutralize with sodium hydroxide standard solution to light red), titrate with sodium hydroxide standard solution to light red as the endpoint, record the volume V of sodium hydroxide standard solution consumed.

[0098] Titration of sodium hydroxide standard solution of the blank sample: the steps are the same as those of the titration of sodium hydroxide standard solution of the digested sample, except that the digested sample is not added, a blank sample is prepared, and the volume V0 of sodium hydroxide standard solution consumed by the blank sample is recorded.

[0099] The silicon content is calculated according to the following formula: ω Si = (V-V0) x c x 7.02 / m x 100%, where: c is the concentration of sodium hydroxide standard solution, in mol / L; V is the volume of sodium hydroxide standard solution consumed, in L; V0 is the volume of sodium hydroxide standard solution consumed by the blank, in L; 7.02 is the molar mass of 1 / 4 Si, in g / mol; m is the mass of the sample, in g.

[0100] Specific surface area test

[0101] The specific surface area of the silicon-based particles of each example and the comparative example was tested by nitrogen adsorption method using a specific surface area analyzer (TriStar II 3020M, USA Micromeritics). The specific test was performed in accordance with the national standard GB / T 19587-2017 "Gas adsorption BET method for determination of specific surface area of solid substances".

[0102] Particle size test

[0103] The Dv50 and Dv90 of the silicon-based particles and the negative electrode material were measured by using a Mastersizer 3000 particle size tester produced by Malvern.

[0104] Calculation of the mass percentage content of carbon element, polymer, first conductive material and second conductive material

[0105] The mass of the silicon-based particles was denoted as W0, the mass of the first intermediate body coated with the first layer of the silicon-based particles was denoted as W1, the mass of the negative electrode material coated with the second layer and the third layer of the first intermediate body was denoted as W2, the mass percentage content of carbon element in the first layer of the negative electrode material was denoted as W C =(W1-W0) / W2x100%.

[0106] The mass percentage content of the polymer was denoted as W J =the mass of the polymer added in the preparation process / W2.

[0107] The mass percentage content of the first conductive material was denoted as W D1 =the mass of the first conductive material added in the preparation process / W2.

[0108] The mass percentage content of the second conductive material was denoted as W D2 =the mass of the second conductive material added in the preparation process / W2.

[0109] Mass percentage content test of metal oxide

[0110] The content of aluminum element or titanium element in the negative electrode material was obtained by ICP element detection, which was converted into the mass percentage content of corresponding aluminum oxide or titanium oxide W M .

[0111] Negative electrode material resistivity test

[0112] The resistivity of the negative electrode material in each example and the comparative example was tested by using a powder resistivity meter in a dry room.

[0113] Preparation of button-type half-cell

[0114] (1) The negative electrode material, acetylene black and sodium alginate prepared in each example or comparative example were added into deionized water according to a mass ratio of 80:10:10, and a slurry with a solid content of 40% was formed after sufficient stirring. The slurry was coated on a copper foil with a thickness of 8 μm by using a doctor blade to form a coating layer with a thickness of 100 μm, and then dried in a vacuum drying oven at 85°C for 12 hours. The dried coating layer was cut into a circular sheet with a diameter of 1 cm in a dry environment by using a punch machine to obtain a positive electrode.

[0115] Electrolyte and separator: ethylene carbonate (EC) and dimethyl carbonate (DMC) were mixed uniformly in a volume ratio of 1:1 to obtain a mixed solution, 1 mol / L LiPF6 and 5 vol% fluoroethylene carbonate (FEC) were added into the mixed solution and stirred uniformly to obtain an electrolyte. A polyethylene film with a thickness of 12 μm was used as a separator.

[0116] (2) Assembly of button-type half cell:

[0117] The above positive electrode was used as a cathode, and a lithium metal sheet was used as an anode. The button-type half cell was assembled in a glove box in the order of positive electrode, separator and lithium metal sheet, and the above electrolyte was added.

[0118] First lithium intercalation expansion rate test

[0119] Before assembling the button-type half cell, the thickness H0 of the positive electrode was measured by using a micrometer. The prepared button-type half cell was discharged at a rate of 0.1C to 0.01V under the conditions of 25°C and normal pressure, and then rested for 30 min. The button-type half cell was disassembled in a glove box, and the thickness H1 of the positive electrode after full lithium intercalation was measured by using a micrometer. The first lithium intercalation expansion rate of the positive electrode of the button-type half cell was (H1-H0) / H0 x 100%.

[0120] First charge-discharge specific capacity test

[0121] The prepared button-type half cell was discharged at a rate of 0.1C to 0.01V under the conditions of 25°C and normal pressure, and then rested for 5 min. The discharge specific capacity at this time was recorded, which was the first discharge specific capacity. Then, the button-type half cell was charged at a rate of 0.1C to 1.5V, and then charged at a constant voltage of 1.5V until the current was 0.05C. After resting for 5 min, one cycle of charge-discharge process was completed. The charge specific capacity at this time was recorded, which was the first charge specific capacity. The first charge-discharge efficiency was (first charge specific capacity / first discharge specific capacity) x 100%.

[0122] Cycle performance test and expansion rate test

[0123] The original thickness of the lithium ion battery was measured by using a micrometer before the test. The lithium ion battery was charged at 3.4C constant current to 4.4V, then charged at 4.4V constant voltage to 0.025C, and discharged at 0.5C constant current to 3.0V after 5 minutes of rest at the test temperature of 25°C and 45°C. The capacity obtained in this step was the initial capacity of the lithium ion battery. The capacity decay curve was obtained by taking the ratio of the capacity of each step to the initial capacity. The cycle performance of the lithium ion battery at room temperature was characterized by the number of cycles at 25°C until the capacity retention rate was 90%, and the cycle performance of the lithium ion battery at high temperature was characterized by the number of cycles at 45°C until the capacity retention rate was 80%. The above cycles were carried out at 25°C and 45°C to the 600th cycle to obtain Figure 2 and Figure 3 i.e. the cycle performance comparison chart of the lithium ion battery at 25°C and the cycle performance comparison chart of the lithium ion battery at 45°C.

[0124] The thickness of the lithium ion battery discharged to 3.0V was measured at 25°C and 45°C after cycling to 400 cycles, respectively. The relative difference between the thickness of the lithium ion battery discharged to 3.0V at 25°C after cycling to 400 cycles and the original thickness of the lithium ion battery, and the ratio of the original thickness of the lithium ion battery, characterized the cycle expansion rate of the lithium ion battery at room temperature. The relative difference between the thickness of the lithium ion battery discharged to 3.0V at 45°C after cycling to 400 cycles and the original thickness of the lithium ion battery, and the ratio of the original thickness of the lithium ion battery, characterized the cycle expansion rate of the lithium ion battery at high temperature. The above cycles were carried out at 25°C and 45°C to the 500th cycle to obtain Figure 4 and Figure 5 i.e. the expansion rate comparison chart of the lithium ion battery at 25°C and the thickness expansion rate comparison chart of the lithium ion battery at 45°C.

[0125] At 25°C, the lithium ion battery was subjected to small rate charging and discharging when cycled to the 2nd, 4th, 50th, 100th, 150th, 200th, 300th, 400th, and 500th cycles. The process was as follows: the lithium ion battery was charged at 0.7C constant current to 4.53V, then charged at 4.53V constant voltage to 0.05C, and discharged at 0.2C constant current to 3.0V after 5 minutes of rest, and then the next cycle was continued.

[0126] High temperature storage performance test

[0127] The lithium ion battery was discharged at 0.5C to 3.0V at 25℃, and then charged to 4.4V at 0.5C, and then constant voltage charged to 0.05C at 4.4V. The thickness of the lithium ion battery at this time was measured using a PPG lithium ion battery thickness gauge, and was recorded as a. The lithium ion battery was placed in a 45℃ oven, and stored at 45℃ under constant voltage 4.4V for 400 hours. The thickness after 400 hours was recorded as b. The high-temperature storage performance of the lithium ion battery was characterized by the storage thickness expansion rate, and the calculation formula of the storage thickness expansion rate was: (b-a) / a x 100%.

[0128] Example 1-1

[0129] Preparation of the negative electrode material

[0130] (1) 200 kg of silicon-carbon particles were taken and subjected to classification treatment using a fluidized bed, to obtain silicon-based particles having a silicon content of 50.1%, a specific surface area of 7.2 m 2 / g, a particle size Dv50 of 1.97 μm, and a Dv90 of 7.4 μm.

[0131] (2) 20 kg of the classified silicon-based particles were transferred into a fluidized bed by high-pressure transmission. After standing for 30 min, the inlet valve and the exhaust valve of the fluidized bed were closed and vacuumized. When the cavity pressure reached -101 kPa, the vacuumization was stopped and nitrogen was introduced at a rate of 100 L / min to positive pressure. The vacuumization and nitrogen introduction were repeated for more than 5 times, and then the oxygen content in the cavity was detected. When the oxygen content was reduced to below 10 ppm, the exhaust valve was opened, the stirring paddle of the fluidized bed was started at a speed of 150 rpm, and nitrogen was introduced at a rate of 200 L / min. The temperature was raised to 550℃ at a rate of 5℃ / min, and the temperature was maintained for 1 h. After the temperature maintenance was completed, the inlet valve of the fluidized bed was switched, and acetylene / nitrogen mixed gas was introduced into the fluidized bed. The volume fraction of acetylene was 25%, and the gas flow rate was 200 L / min. The reaction time was 150 min. After the reaction was completed, nitrogen was introduced at a flow rate of 150 L / min, the stirring paddle speed was adjusted to 100 rpm, and the temperature was lowered to room temperature for discharge. The first intermediate was obtained.

[0132] (3) Take 10 L of anhydrous ethanol, and add 2 kg of the first intermediate powder, 40 g of aluminum isopropoxide, 40 g of polyvinylpyrrolidone, and 1 kg of a single-walled carbon nanotube ethanol slurry with a solid content of 1.2% (the single-walled carbon nanotube content is 0.4%, and 0.8% is a dispersant) to the anhydrous ethanol while stirring. After 4 h of sufficient stirring, a first dispersion is obtained. The addition amount of aluminum isopropoxide is 2% and the addition amount of single-walled carbon nanotubes is 0.2% based on the mass of the first intermediate. Start the spray dryer, set the inlet air temperature to 180°C and the outlet air temperature to 95°C, and after the inlet air temperature and the outlet air temperature reach the set range, first supply anhydrous ethanol at a supply rate of 70 mL / min. After stable operation for 30 min, switch to supply the first dispersion. The dried powder obtained from the outlet is loaded into a graphite crucible, which is placed in a box furnace. After closing the chamber door, nitrogen is passed at a flow rate of 2 L / min for 30 min, then heating is started. The temperature is raised to 550°C at a rate of 5°C / min, and then held for 1 h. After the heating is turned off and the nitrogen is continued to be passed until the temperature cools to room temperature, the crucible is taken out, and a heat-treated second intermediate powder is obtained.

[0133] (4) Take 6 kg of deionized water, and add 2 kg of the second intermediate powder to the deionized water while stirring to obtain a second dispersion. Add 180 g of polyurethane and 20 g of single-walled carbon nanotubes to 800 g of deionized water to obtain a third dispersion with a solid content of 20%. After the second dispersion is stirred for 2 h, 0.5 kg of the third dispersion is added to the second dispersion while stirring, and the mixture is stirred for 3 h. A mixed slurry of the second dispersion and the third dispersion is obtained. The addition amount of polyurethane is 4.5% and the addition amount of single-walled carbon nanotubes is 0.5% based on the mass of the second intermediate. Start the spray dryer, set the inlet air temperature to 220°C and the outlet air temperature to 105°C, and the atomizing disc rotation speed to 16500 rpm. After the inlet air temperature and the outlet air temperature reach the set range, first supply deionized water at a supply rate of 300 mL / min. After stable operation for 30 min, switch to supply the mixed slurry. The dried negative electrode material is obtained from the outlet. Among them, based on the mass of the negative electrode material, the mass percentage of carbon in the first layer is 3%, the mass percentage of aluminum oxide is 0.44%, the mass percentage of the first conductive material is 0.18%, the mass percentage of polyurethane is 4.32%, and the mass percentage of the second conductive material is 0.48%. The Dv50 of the negative electrode material is 7.8 μm, and the Dv90 is 27 μm.

[0134] The structural schematic diagram of the negative electrode material prepared in Example 1-1 is shown in Figure 1 .

[0135] Examples 1-2 to 1-11

[0136] The rest was the same as Example 1-1 except that the mass percentage content of carbon in the first layer, the mass percentage content of metal oxide in the second layer, the mass percentage content of the first conductive material, the mass percentage content of polyurethane, the mass percentage content of the second conductive material, and the mass ratio of polyurethane and the second conductive material were adjusted according to Table 1 in the preparation of the negative electrode material.

[0137] Example 1-12

[0138] The rest was the same as Example 1-1 except that the silicon content of the silicon oxide particles was 49.4%, the specific surface area was 3.8 m 2 / g, Dv50 was 2.1 μm, and Dv90 was 7.5 μm in the preparation of the negative electrode material.

[0139] Example 1-13

[0140] The rest was the same as Example 1-1 except that titanium isopropoxide was used instead of aluminum isopropoxide in the preparation of the negative electrode material.

[0141] Example 1-14

[0142] The rest was the same as Example 1-1 except that multi-walled carbon nanotubes were used instead of single-walled carbon nanotubes as the first conductive material in the preparation of the negative electrode material.

[0143] Example 1-15

[0144] The rest was the same as Example 1-1 except that conductive carbon black was used instead of single-walled carbon nanotubes as the first conductive material in the preparation of the negative electrode material.

[0145] Example 1-16

[0146] The rest was the same as Example 1-1 except that multi-walled carbon nanotubes were used instead of single-walled carbon nanotubes as the second conductive material in the preparation of the negative electrode material.

[0147] Example 1-17

[0148] The rest was the same as Example 1-1 except that conductive carbon black was used instead of single-walled carbon nanotubes as the second conductive material in the preparation of the negative electrode material.

[0149] Example 2-1

[0150] Preparation of the negative electrode

[0151] The graphite, the negative electrode material prepared in Example 1-1, a conductive agent (conductive carbon black, Super P) and a binder (polyacrylic acid (PAA)) were mixed in a solvent (deionized water) in a mass ratio of 80:10:5:5 to prepare a negative electrode slurry with a solid content of 70 wt%, deionized water was added, and the viscosity of the slurry was adjusted to 5000 Pa·s to prepare a negative electrode slurry. The negative electrode slurry was uniformly coated on one surface of a negative electrode current collector copper foil with a thickness of 6 μm, and dried at 120°C to obtain a negative electrode sheet with a single-side coated negative electrode material layer, and the coating weight of the negative electrode material layer was 142 mg / 1540 mm 2 . Then the above steps were repeated on the other surface of the copper foil to obtain a negative electrode sheet with a double-side coated negative electrode material layer. After drying at 120°C and cold pressing, the negative electrode sheet was cut and the tab was welded to obtain a negative electrode sheet with a size of 78 mm x 875 mm for use. The thickness of the single-side negative electrode material layer was 54.5 μm.

[0152] <Preparation of a positive electrode>

[0153] The positive electrode active material LiCoO2, conductive carbon black and polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 95:2.5:2.5 in an N-methylpyrrolidone solvent system to prepare a positive electrode slurry. The positive electrode slurry was uniformly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 10 μm, and dried at 120°C to obtain a positive electrode sheet with a single-side coated positive electrode material layer, and the coating weight of the positive electrode material layer was 267.8 mg / 1540 mm 2 . Then the above steps were repeated on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-side coated positive electrode material layer. After drying at 120°C and cold pressing, the positive electrode sheet was cut and the tab was welded to obtain a positive electrode sheet with a size of 74 mm x 867 mm for use. The thickness of the single-side positive electrode material layer was 42 μm.

[0154] <Preparation of an electrolyte>

[0155] In a dry argon environment, propylene carbonate (PC), ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed in a mass ratio of 1:1:1 to obtain a base solvent, and lithium salt LiPF6 was added and mixed uniformly to dissolve and mix uniformly to obtain an electrolyte; wherein the mass percentage of lithium salt LiPF6 based on the total mass of the electrolyte was 12.5%, and the balance was the base solvent.

[0156] <Separator>

[0157] A polyethylene / polypropylene composite film with a thickness of 8 μm was used as a separator.

[0158] <Preparation of a lithium ion battery>

[0159] The positive electrode, the separator, and the negative electrode are stacked in order, with the separator between the positive electrode and the negative electrode to play a separating role, to obtain a bare battery cell; after the tab is welded, the bare battery cell is placed in an outer packaging aluminum plastic film, the above-prepared electrolyte is injected into the dried bare battery cell, and the lithium ion battery is obtained through a process flow of vacuum packaging, standing, formation, shaping, degassing, and capacity testing.

[0160] Examples 2-2 to 2-17

[0161] The rest is the same as Example 2-1, except that the negative electrode material prepared in <Preparation of the negative electrode> is prepared by using Examples 1-2 to 1-17.

[0162] Examples 3-1 to 3-11

[0163] The rest is the same as Example 2-1, except that the additive is added to the electrolyte according to Table 3 in <Preparation of the electrolyte>, and the mass percentage of the additive is adjusted, the mass percentage of the base solvent is changed accordingly, the mass ratio of each component of the base solvent remains unchanged, and the mass percentage of lithium salt LiPF6 remains unchanged.

[0164] Comparative Example 1

[0165] The rest is the same as Example 1-1, except that the silicon-based particles are not coated in <Preparation of the negative electrode material>, and the specific data are shown in Table 1.

[0166] Comparative Example 2

[0167] The rest is the same as Example 1-1, except that the silicon-based particles do not have a second layer in <Preparation of the negative electrode material>, and the specific data are shown in Table 1.

[0168] Comparative Example 3

[0169] The rest is the same as Example 1-1, except that the silicon-based particles do not have a third layer in <Preparation of the negative electrode material>, and the specific data are shown in Table 1.

[0170] Comparative Examples 4 to 6

[0171] The rest is the same as Example 2-1, except that the negative electrode material prepared in <Preparation of the negative electrode> is prepared by using Comparative Examples 1, 2, and 3 in turn.

[0172] The preparation parameters and performance tests of each example and comparative example are shown in Tables 1 to 3.

[0173]

[0174]

[0175] As can be seen from Examples 1-1 to 1-17, Examples 2-1 to 2-17 and Comparative Examples 1 to 6, when the negative electrode material has the three-layer coating structure of the present application, the negative electrode material has a lower resistivity, a higher silicon content, and has a higher first charge-discharge efficiency and a lower first full lithium intercalation expansion rate; the obtained lithium ion battery has a higher cycle number and a lower lithium ion battery expansion rate at room temperature and high temperature, thereby indicating that the cycle performance of the lithium ion battery is improved and the expansion rate is reduced.

[0176] As can be seen from the description of the accompanying drawings Figures 2-3 , the negative electrode material in Example 1-1 is applied to a lithium ion battery, and compared with Comparative Examples 4 to 6, the lithium ion battery has a higher cycle capacity retention rate after being cycled to 200 cycles at room temperature and high temperature. As can be seen from the description of the accompanying drawings Figures 4-5 , the lithium ion battery of Example 2-1 has a lower thickness expansion rate after being cycled to 200 cycles, and thus the cycle performance and expansion performance of the lithium ion battery of Example 2-1 are superior to those of Comparative Examples 4 to 6.

[0177] As can be seen from Examples 1-1 to 1-17, Examples 2-1 to 2-17, when the silicon content of the negative electrode material is 40% to 50%, the Dv50 is 6 μm to 10 μm, the Dv90 is less than or equal to 30 μm, the mass percentage content W C of carbon in the first layer is 1% to 5%, the mass percentage content W M of metal oxide is 0.2% to 1%, the mass percentage content W D1 of the first conductive material is 0.1% to 0.4%, the mass percentage content W J of polyurethane is 0.9% to 9%, and / or the type mass percentage content W D2 of the second conductive material is 0.1% to 1%, the negative electrode material has a lower resistivity, a higher silicon content, and has a higher first charge-discharge efficiency and a lower first full lithium intercalation expansion rate; the obtained lithium ion battery has a higher cycle number and a lower lithium ion battery expansion rate at room temperature and high temperature, thereby indicating that the cycle performance of the lithium ion battery is improved and the expansion rate is reduced.

[0178] Table 3

[0179]

[0180] Note: " / " in Table 3 means that the corresponding preparation parameter or substance does not exist.

[0181] The type and content of additives in the electrolyte typically affect the cycle performance and high-temperature storage performance of lithium-ion batteries. As can be seen from Examples 1-1, 3-1 to 3-11, introducing the additives of this application into the electrolyte results in higher cycle counts and lower storage thickness expansion rates for lithium-ion batteries compared to Example 1-1 without additives, thus demonstrating improved cycle performance. When the additive content is between 1% and 3%, the cycle performance of the lithium-ion battery is further enhanced.

[0182] The terms “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, or article that comprises a list of elements includes not only those elements but also other elements not expressly listed or inherent to such process, method, or article.

[0183] The various embodiments in this specification are described in a related manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

[0184] The above description is only a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the principles of this application should be included within the scope of protection of this application.

Claims

1. A negative electrode material comprising: The core comprises silicon-based particles; The first layer exists outside the kernel; The second layer exists outside the first layer; The third layer exists outside the second layer; in, The first layer contains carbon; the second layer contains a first conductive material and a metal oxide; and the third layer contains a second conductive material and a polymer.

2. The negative electrode material according to claim 1, wherein, The silicon-based particles include at least one of silicon-carbon particles or silicon-oxygen particles; or the metal oxide includes at least one of aluminum oxide or titanium oxide; or the polymer includes polyurethane; or the first conductive material and the second conductive material are each independently selected from at least one of single-walled carbon nanotubes, multi-walled carbon nanotubes, or conductive carbon black.

3. The negative electrode material according to claim 1, wherein, Based on the mass of the negative electrode material, the silicon content is 40% to 50% by mass.

4. The negative electrode material according to any one of claims 1 to 3, wherein, The negative electrode material satisfies at least one of the following: (1) The Dv50 of the negative electrode material is 6 μm to 10 μm; (2) The Dv90 of the negative electrode material is less than or equal to 30 μm; (3) Based on the mass of the negative electrode material, the mass percentage of carbon in the first layer is 1% to 5%; (4) Based on the mass of the negative electrode material, the mass percentage of the metal oxide is 0.2% to 1%; (5) Based on the mass of the negative electrode material, the polymer has a mass percentage content of 0.9% to 9%; (6) Based on the mass of the negative electrode material, the mass percentage of the first conductive material is 0.1% to 0.4%; (7) Based on the mass of the negative electrode material, the mass percentage of the second conductive material is 0.1% to 1%.

5. The negative electrode material according to claim 4, wherein, The mass ratio of the polymer to the second conductive material is 9:1 to 9:

2.

6. A method for preparing the negative electrode material according to any one of claims 1 to 5, comprising: Provides silicon-based particles; The silicon-based particles are carbon-coated to obtain a first intermediate. The first intermediate, organometallic salt, polyvinylpyrrolidone and the first conductive material are dispersed in ethanol to obtain a first dispersion. The first dispersion is fully dispersed and stirred, and then spray-dried and heat-treated at 500°C to 600°C to obtain a second intermediate. The organometallic salt includes at least one of aluminum isopropoxide or titanium isopropoxide. The second intermediate is dispersed in water to obtain a second dispersion. The polymer and the second conductive material are dispersed in water to obtain a third dispersion. The second dispersion and the third dispersion are mixed and stirred evenly, and the negative electrode material is obtained by spray drying.

7. The preparation method according to claim 6, wherein, The carbon coating process involves placing silicon-based particulate material in a fluidized bed, introducing a carbon source gas at a temperature of 500°C to 600°C, and reacting for 2 to 3 hours to obtain a first intermediate. The carbon source gas includes at least one of acetylene, methane, and propylene.

8. An electrochemical device comprising a positive electrode, a separator, an electrolyte, and a negative electrode, wherein the negative electrode comprises a negative electrode active material layer comprising the negative electrode material according to any one of claims 1 to 5.

9. The electrochemical device according to claim 8, wherein, The electrolyte includes an additive comprising at least one of 1,3,6-hexanetrionitrile, 1,2,3-propanetrimethylonitrile, or 1,2,3-tris(2-cyanoxy)propane, wherein the additive comprises 0.1% to 5% by mass based on the total mass of the electrolyte.

10. An electrical device comprising the electrochemical device according to any one of claims 8 to 9.

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